NERVUS TERMINALIS IN REPTILE AND MAMMAL 101 



The ganglion is more compact arid lies in the angle between the 

 olfactory bulb and the forebrain proper. Peripherally the strands 

 of the nerve pass through a depression in the medial wall of the 

 olfactory sac, diverge a little from one another and converge 

 again slightly to end in the wall of the vomero-nasal organ. One 

 strand passes to the nasal sac rostral to the vomero-nasal organ. 



In figure 2 are shown the ganglion and root as they appear 

 in sagittal section of a 19 mm. embryo. The root fibers as they 

 pass caudad in the brain wall are accompanied by slender elon- 

 gated cells. 



In the 53 mm. embryo the differentiation of gray masses in 

 the brain has gone far enough to make it possible to determine 

 the general relations of the root. In figure 6 A, which represents 

 a transverse section of the rostral end of the forebrain, the medio- 

 dorsal cortex is seen extending down in the medial wall of the 

 hemisphere and ending abruptly. The lower portion of this 

 medial cortex is the developing hippocampus. Below it is the 

 precommissural or paraterminal body of Elliot Smith. The 

 boundary line between the two corresponds to the zona limitans 

 which separates the hippocampal primordium from the precom- 

 missural body in such primitive forms as selachians. In this 

 section the root of the nervus terminalis is seen enter" ng the 

 brain a little below the border of the hippocampal cortex. The 

 16 mm. pig (fig. 5 A) shows the nerve just above the tuberculum 

 olfactorium. As the writer has shown elsewhere ('11), the nervus 

 terminalis in certain typical selachians follows the zona limitans 

 and is lost in the brain substance near the neuroporic recess. 

 It is therefore clear that the nervus terminalis enters the brain 

 in the pig in the same relations as in selachians. Peripherally the 

 nerve in the 53 mm. pig bears essentially the same relations as 

 in the younger stage described. The ganglion is more slender 

 and the nerve gives the appearance of being reduced in size 

 actually as well as relatively. 



I have not yet been fortunate in securing a Golgi impregnation 

 of the root of this nerve in the pig. Peripherally it takes the 

 silver impregnation fairly well and its distribution to the vomero- 

 nasal organ has been verified by this method. A few bipolar 



